Recently, vehicles such as automobiles are installed with an in-vehicle control apparatus constituting a navigation system and in-vehicle control apparatuses for electronically controlling various in-vehicle devices such as an engine and a brake. Vehicles are also installed with many other in-vehicle control apparatuses, such as in-vehicle control apparatuses for controlling devices such as meters that display various conditions of the vehicle. A vehicle network is formed by electrically connecting the respective in-vehicle control apparatuses using a communication line, and various types of vehicle data are exchanged between the respective in-vehicle control apparatuses via the vehicle network.
Meanwhile, as vehicles become ever more sophisticated, the number of in-vehicle control apparatuses constituting the vehicle network tends to increase. With this increase in the number of in-vehicle control apparatuses, or in other words a number of nodes, a communication load of the vehicle network may increase to the extent that communication delays and the like occur.
Hence, an apparatus described in Patent Document 1, for example, calculates a standard deviation of a transmission period of data transmitted to a vehicle network and, when the transmission period of data having a high predefined priority level is shorter than the standard deviation, performs processing to reduce an amount of communication data transmitted to the vehicle network. In so doing, when data having a high priority level are transmitted frequently, the load on the vehicle network can be reduced, and as a result, the data having a high priority level can be transmitted with stability.
Patent Document 1: Japanese Patent Application Publication No. 2010-28355